1. Field of the Invention
The present invention relates to a motor having a suction ring, particularly, relates to a motor having a suction ring suitable for driving a hard disc drive and a laser beam printer.
2. Description of the Related Art
A motor for driving a hard disc drive (hereinafter referred to as HDD) according to the prior art is shown in FIG. 5.
FIG. 5 is a cross sectional view of a motor according to the prior art, and FIG. 6 is a plan view of a suction ring to be used in the motor shown in FIG. 5.
In FIG. 5, a motor 150 is driven by three-phase current and mounted with at least one hard disc (HD) 101 thereon.
Further, the motor 150 is essentially composed of a stator S1 and a rotor R1.
The stator S1 is further composed of a core 106, a coil 107, a counter plate 109, a sleeve 110 and a motor base 105. The motor base 105 is formed by a process of pressing an aluminum plate or an aluminum die-casting process.
The sleeve 110 is in a cylindrical shape and fixed on a circumferential wall surface of a hole formed vertically in the center of the motor base 105 by a binding agent or a press fitting process.
Further, an inner circumferential section of the sleeve 110 is made from a sintered metal material or a plated copper alloy material.
Furthermore, one end portion of the sleeve 110 is formed with a stepped section for containing a thrust ring 112 to be detailed and the end portion is sealed by the counter plate 109.
As mentioned above, the motor 150 is driven by the three-phase current, so that the core 106 is provided with nine protrusions equivalent to magnetic poles and formed in approximately an annular shape.
More specifically, the core 106 is formed by laminating a plurality of silicon steel plates and a surface of the core 106 is treated by insulation coating through a process such as electropainting and powder coating.
Further, each protrusion of the core 106 is wound up by the coil 107.
Furthermore, a terminal 107a of a winding wire of the coil 107 is soldered on a flexible printed circuit board (hereinafter referred to as FPC) 114 mounted on a bottom of the motor base 105 by way of a through hole 121.
On the other hand, the rotor R1 is further composed of a hub 102, a shaft 113 and a magnet 108.
The hub 102 and the shaft 113 are made from a stainless steel material through a cutting process.
The magnet 108 is formed in a ring shape (hereinafter referred to as ring magnet 108) and made from an Nd—Fe—B system material. A surface of the ring magnet 108 is treated by an electropainting process.
Further, the shaft 113 is fixed to the hub 102 through a process of press fitting and then adhered.
Furthermore, the ring magnet 108 is fixed on an inner surface of an outer circumferential section of the hub 102 by a binding agent.
In addition thereto, the motor 150 is provided with a thrust dynamic pressure fluid bearing SB1 and radial dynamic pressure fluid bearings RB11 and RB12.
The thrust dynamic pressure fluid bearing SB1 is constituted by the thrust ring 112 in an annular shape that is fixed on a lower end portion of the shaft 113, the sleeve 110, the counter plate 109 and lubricating fluid (hereinafter referred to as lubricant) that is filled among each member.
The thrust ring 112 is made from a stainless steel material or a copper alloy. In case the thrust ring 112 is made from a copper alloy, surfaces of the thrust ring 112 are nickel-plated.
Under the above-mentioned configuration, the thrust dynamic pressure fluid bearing SB1 sustains the rotor R1 in the thrust direction by generating dynamic pressure in the thrust direction by means of dynamic pressure grooves formed on both the top and bottom surfaces of the thrust ring 112 while the rotor R1 is rotating.
On the other hand, the radial dynamic pressure fluid bearings RB11 and RB12 are constituted by an outer circumferential surface of the shaft 113, an inner circumferential surface of a through hole of the sleeve 110 into which the shaft 113 is inserted, and lubricant filled in a gap between them.
At least either one of the outer circumferential surface of the shaft 113 and the inner circumferential surface of the sleeve 110 is formed with radial dynamic pressure grooves such as herringbone for generating dynamic pressure. The dynamic pressure grooves generate dynamic pressure in the radial direction while the rotor R1 is rotating, and result in sustaining the rotor R1 in the radial direction. Two groups of radial dynamic pressure grooves are provided at two individual positions being apart from each other along the axis of rotation.
Further, the inner circumferential section of the sleeve 110 is made from a sintered material or a plated copper alloy material, as mentioned above, and provided with a recessed portion that is disposed between the two individual positions being formed with radial dynamic pressure grooves. In some cases, the sleeve 110 is divided into two components.
As mentioned above, the gap between the shaft 113 and the sleeve 110 and each gap among the thrust ring 112, the sleeve 110 and the counter plate 109 are filled with lubricant such as lubrication oil. The lubricant is circulated by the revolution of the rotor R1, and resulting in generating dynamic pressure. By the dynamic pressure, each dynamic pressure fluid bearing sustains the rotor R1 to be rotatable freely.
In the meantime, the motor 150 is installed with a suction ring 111 that is formed in a flat annular shape and disposed on the top surface of the motor base 105. A plan view of the suction ring 111 is shown in FIG. 6. Such a motor installed with a suction ring is disclosed in the Japanese publication of unexamined patent applications No. 2003-61305.
The suction ring 111 is made from iron that is a magnetic material and disposed under the ring magnet 108 so as to confront at least a part of the suction ring 111 with the bottom surface of the ring magnet 108.
Accordingly, the rotor R1 is magnetically absorbed toward the stator S1 side and restricted its movable distance in the axial direction.
Installing such a suction ring enables to ensure higher anti-vibration ability and higher impact resistant, which are particularly required for a motor to be installed in an HDD.
In case such a suction ring is adhered on a motor base by using a binding agent, the suction ring may rise or slant with respect to the motor base due to shrinkage of the binding agent when hardening.
If such rising of the suction ring occurs, uniform suction force is not ensured, and resulting in generating a problem of deteriorating noise level and vibration level of the motor.
Further, if the rising of the suction ring is excessively increased, the suction ring possibly contacts with a ring magnet and adds rotational load to the rotor, and resulting in generating another problem of increasing power consumption of the motor.
In this connection, it is commonly adopted as a method for installing a suction ring not to rise that an outer circumferential section of the suction ring is press fitted to an inner surface of a circular wall section provided for the motor base.
However, such a press fitting method creates further problems to be mentioned next, so that the method has been desired to be improved.
Generally, a binding agent is used for fixing several components together when assembling a motor. In order to harden the binding agent completely and to prevent so-called “out-gas” phenomenon that is a phenomenon of generating gas from the hardened binding agent with time, a treatment of so-called burning is applied to a motor, wherein the treatment of burning is such as leaving a motor after assembled in a high temperature ambience of 130° C.
As mentioned above, the motor base is made from aluminum. A coefficient of linear expansion of the aluminum is 23.5×10−6/° C. On the contrary, the suction ring is made from iron, and a coefficient of linear expansion of the iron is 12.1×10−6/° C. As a matter of fact, each coefficient of linear expansion extremely differs from each other.
Accordingly, dimensional change in the radial direction caused by thermal expansion extremely reduces an overlap width for press fitting between the motor base and the suction ring, and resulting in generating a furthermore problem of rising the suction ring unless each overlap width of the suction ring and the motor base is designated to be more than a prescribed value.
As a specific example, with respect to a suction ring having a thickness of 0.4 mm, in case a diameter of an outer circumferential section of the suction ring to be press fitted into a motor base is designated to be 20 mm, an overlap width for press fitting disappears during the treatment of burning, and resulting in raising the suction ring unless the suction ring is press fitted into the motor base with being previously provided with an overlap width of 25 μm or more in diameter at the normal temperature (20° C.).
However, in order to actually press fit the above-mentioned members while maintaining the overlap width of 25 μm or more in diameter for press fitting, it is necessary for press fitting pressure to be more than 86 N. Enabling such a press fitting process of more than 86 N requires a relatively large-scale facility. In some cases, the motor base is deformed by such a high press fitting pressure, and resulting in deteriorating noise level and vibration level of a motor to be assembled.
Further, in case the suction ring is press fitted by such a high press fitting pressure, the suction ring disables to be accurately disposed in a prescribed position, and resulting in making a distance between the ring magnet and the suction ring uneven. Under such a circumstance, a movable distance in the axial direction of the rotor fluctuates, and resulting in generating a more problem of deteriorating noise level and vibration level of the motor.
In case the press fitting pressure is 20 N or less, the press fitting process enables to be performed by a regular facility.
In addition thereto, the pressure of 20 N or less is preferable because deformation of members other than the press fitted section never occurs or deformation is extremely slight if occurred.